Task: Replace a Faulty PLA Chip in a Commodore 64 with a PLA20V8
Needed: PLA20V8
Time: 15-30 minutes
Introduction
The Programmable Logic Array or PLA is key to managing the chips using the data bus in the Commodore 64. Unfortunately, the MOS-branded PLAs are prone to failure. The good news is that there are several different replacements available including an inexpensive option based on the readily available GAL20V8 chip that can be programmed to replace the functionality of the PLA. This PLA20V8 is a drop-in replacement that several vendors offer for sale online. It is possible to make your own PLA20V8 as documented here, here, and in this YouTube video. I have not made one yet myself and will save that for a future project.
Instructions
There are several places to purchase the PLA20V8 (aka GAL PLA). I purchased mine for about $15 from 8-Bit Classics. eBay has several sellers. Here is a SlimPLA with a nice slimmer form for $20. Here is PLA20V8 for $15. Here is a cheaper one from the USA for $12.50.
Simply replace your nonworking PLA with the GAL PLA. You may need to solder in a socket as I did.
Comments
Happy to have this cheap replacement! Mine worked great. I used it to populate a motherboard I am fixing up. Cheaper than buying a real PLA.
Note that the pins are fragile and can break easily. Be very careful taking these in and out of sockets.
